The invention relates to an agricultural harvesting machine (e.g., a forage harvester) configured with a comminution assembly having a drum equipped with a plurality of knives that is set into rotation opposite a stationary shear bar in order to comminute crop fed in the region of a cutting gap formed by knives and shear bar during the harvesting operation, and more particularly relates to such a machine that includes a device for controlling the rotational speed (n) of the drum at least during a maintenance procedure of the comminution assembly depending on a property of the drum.
During operation of an agricultural harvesting machine, such as a forage harvester in particular, various maintenance actions must be repeatedly performed on the chopping assembly within the scope of the harvesting operation in order to maintain the quality of the chopping process. The reason therefor is that the cutting process to which the incoming crop is continuously subjected induces wear on the chopping knives and on the shear bar of the chopping assembly. If chopping is performed using blunt knives and/or with a shear bar that is imprecisely adjusted, for whatever reason, this in turn results in reduced chopping quality and increased energy consumption for driving the chopping assembly.
It is therefore necessary to perform maintenance actions on the chopping assembly comprising in particular sharpening the knives and/or precisely adjusting the shear bar in order to obtain a suitable cutting gap.
According to conventional methods, both of the aforementioned maintenance procedures are performed while the chopper drum is running. In order to perform sharpening, a sharpening stone is moved parallel to the rotational axis of the (rotating) chopper drum along the chopping knives using a sharpening carriage, and is thereby radially preloaded against the chopping knives in order to apply a sharpening force to the knives. Reference is made in this context to DE 41 28 483 A1, for example.
In order to obtain different lengths of cut, for use with different crop types and/or for other reasons, it is common to equip the chopper drum with different numbers of knives or to use different types of chopper drums having different numbers of knife receptacles (and, therefore, different numbers of knives). In respect of sharpening processes to be carried out, as the distance between successive knives increases, whether due to the design of the chopper drum and/or due to the knife-installation state, the risk also increases that the sharpening stone, which is radially preloaded against the chopper drum, will abruptly drop into the intermediate spaces (gaps) between the knives. This abrupt drop induces strong oscillations, which are expressed as loud, audible, unpleasant noises and also result in premature wear at least of the knives and the sharpening device.
In addition, in order to maintain good chopping quality and prevent increased fuel consumption, the distance between the shear bar and the rotating chopper drum must always be set exactly. This is performed in a manner known per se, for which reference is made to EP 0 291 216 A, for example, within the framework of an adjustment procedure by incrementally moving the shear bar, one side at a time, toward the rotating chopper drum, until knock sensors mounted on the shear bar detect contact by the shear bar with the knives moving past. Due to the sensor system used in this adjustment process and due to other ambient conditions, the knock-sensor signals to be evaluated contain a large noise component. In particular, when chopper drums are equipped with different numbers of knives and/or when different types of cutting cylinders are used, it is difficult for evaluation electronics that are used to detect individual knives from among low-voltage, noisy signals. Noise-induced voltage swings can therefore be easily misinterpreted by being allocated to a knife that is not even present. This problem intensifies in practical applications since an increasing bandwidth of drums and numbers of knives is used and the knock sensors must therefore detect knocking that is triggered with very different timing.